TPA is currently produced via a catalytic and aerobic oxidation of para-xylene (pX), which in turn is produced from fossil resources. TPA is used primarily as a co-monomer in a condensation with mono ethylene glycol to produce poly(ethylene terephthalate) (PET) for plastic bottles, fibers, films, etc. Condensations of TPA with other glycols produce other various polyesters.
Currently, there is strong interest to improve the environmental profile of TPA, either by improving the environmental aspects of the pX oxidation process and/or producing TPA from non-fossil resources (i.e., renewable and inorganic resources; non-fossil-derived TPA), such as carbohydrates, lignin, inorganic salts, etc. More on the current process to produce fossil-derived TPA and pathways to produce non-fossil-derived TPA can be found in Collias et al. (2014) Ind. Biotechnology 10(2): 91-105.
Fossil-derived TPA contributes to greenhouse emissions due to its high fossil-derived carbon content. Furthermore, fossil resources, such as crude oil, natural gas, coal, peat, etc., are considered non-renewable materials, since they take hundreds of thousands of years to form naturally and are consumed quickly. On the other hand, renewable resources refer to materials that are produced via a natural process at a rate comparable to their rate of consumption (e.g., within a 100-year time frame). Renewable resources can be replenished naturally or via agricultural techniques. Examples of renewable resources include plants, such as sugar cane, sugar beets, corn, potatoes, citrus fruit, woody plants, lignocellulose, carbohydrate, hemicellulose, cellulosic waste, animals, fish, bacteria, fungi, and forestry products. Inorganic resources refer to inorganic salts, such as calcium carbonate, etc. As fossil resources become increasingly scarce and more expensive, exhibit higher price volatility, and become subject to regulations for fossil CO2 emissions, there exists a growing need for non-fossil-derived TPA, which can serve as an alternative to fossil-derived TPA. Additionally, as natural gas in the U.S. displaces naphtha as a feedstock for the petrochemical industry, shortages of fossil-derived aromatic materials are expected in the future, and thus there will be an increasing need for non-fossil-derived aromatics.
Many attempts have been made over the last decades to make non-fossil-derived TPA (see Collias et al.). However, no process has yet demonstrated its commercial viability, i.e., high yield of and selectivity for non-fossil-derived TPA, low selectivity for side products, and mild process conditions. Accordingly, there is a need for methods for the production of non-fossil-derived TPA with commercial viability.